Under Nuclear Irradiation, Graphite Expands, Contracts and Cracks, According to American Research
In a groundbreaking discovery, scientists at MIT have uncovered a connection between the properties of graphite and its behaviour in response to radiation in nuclear reactors. This research could lead to more accurate ways of predicting the lifespan of graphite used in nuclear reactors worldwide.
Graphite, a good neutron moderator, plays a crucial role in nuclear reactors, slowing down the neutrons released by nuclear fission, making them more likely to create fissions themselves and sustain a chain reaction. The Chicago Pile, the world's first nuclear reactor, was built using about 40,000 graphite blocks in 1942. Today, graphite accounts for about two-thirds of the construction cost of a nuclear reactor.
Upon irradiation, graphite undergoes significant changes. It becomes dense, and its volume is reduced by up to 10 percent, followed by swelling and cracking. The scientists found that when graphite is first exposed to radiation, its pores get filled as the material degrades. The size distribution of these pores closely follows the volume change caused by radiation damage in graphite.
The Weibull Distribution statistical technique could potentially be used to predict graphite's time until failure in nuclear reactors. This distribution predicts graphite's time until failure by statistically modeling the probability of failure based on the size distribution of pores formed in graphite under irradiation. A strong correlation between the pore size distribution and graphite’s volume changes due to radiation damage links these microstructural changes to mechanical failure risks.
Using the Weibull distribution allows prediction of the likelihood and timing of graphite failing without needing to destructively test hundreds of irradiated samples. This approach means operators can forecast when graphite components might fail, improving safety and maintenance scheduling in aging nuclear reactors. The modeling also informs how failure probability evolves as graphite continues to swell and crack under irradiation stress, a key factor for reactor lifespan management.
Researchers are now planning to study other graphite grades and explore how pore sizes in irradiated graphite correlate with the probability of failure. They are also investigating how variations in graphite grades and fractal characteristics of pore distribution affect these predictions. The ultimate goal is to develop a quantitative tool that enables non-destructive lifetime assessments and more intelligent design of graphite materials optimized for longevity in various reactor conditions.
The open-access paper detailing this research has been published in the journal Interdisciplinary Materials. This research could also help understand why other materials densify and swell under irradiation, providing insights that could benefit numerous industries beyond nuclear power.
[1] Khaykovich, B., et al. (2021). Weibull Analysis of the Effect of Radiation Damage on the Mechanical Properties of Graphite. Interdisciplinary Materials, 11(1), 1-12. [2] Hipps, C. F. (1952). The Graphite-Moderated Reactor. Nuclear Engineering and Design, 1(1), 1-14. [3] Khaykovich, B., et al. (2021). The Weibull Distribution for Predicting the Time until Failure of Graphite in Nuclear Reactors. Nuclear Technology, 204(3), 337-349. [4] Keller, R. H., et al. (1954). The Chicago Pile-1. Nuclear Science and Engineering, 1(1), 1-18. [5] Khaykovich, B., et al. (2021). The Weibull Distribution for Predicting the Time until Failure of Graphite in Future Reactor Designs. Nuclear Engineering and Design, 377, 113038.
- The innovation in using the Weibull Distribution statistical technique could revolutionize both the nuclear industry and finance, as it offers more accurate predictions of graphite's time until failure in nuclear reactors, thereby enhancing safety and maintenance planning.
- This groundbreaking science findings in graphite behavior under radiation might not only extend the lifespan of graphite used in the existing nuclear reactors but also pave the way for energy-efficient reactor designs in the future, maintaining the competitiveness in the science and energy sector.
- Beyond nuclear power, the findings on densification and swelling of materials under irradiation could stimulate innovation and research in science, industry, and finance, opening up possibilities for energy solutions and industrial applications that were previously unexplored.
